A facile one-step hydrothermal approach to synthesize hierarchical core-shell NiFe2O4@NiFe2O4 nanosheet arrays on Ni foam with large specific capacitance for supercapacitors

Porous nanosheet-nanosphere@nanosheet FeNi2-LDH@FeNi2S4 core-shell heterostructures for asymmetric supercapacitors

Transition bimetallic sulphides have emerged as important electrode materials for supercapacitors owing to their low toxicity, environmental friendliness, cost-effectiveness, multiple oxidation states, high natural abundance, flexible structure, and high theoretical specific capacitance. Herein, a porous nanosheet-nanosphere@nanosheet FeNi2-LDH@FeNi2S4 (FNLDH@FNS) core-shell heterostructure was directly prepared on nickel foam (NF) via a two-step hydrothermal method. The prepared electrode material exhibits an outstanding electrochemical performance. The specific capacity (Cs) values are 806 and 450 C g-1 at current density (Dc) values of 1 and 6 A g-1, respectively, revealing a satisfactory magnification performance. In addition, the FNLDH@FNS electrode exhibits a long cycle life with an supercapacitor (SC) retention rate of 92.3% after 5000 cycles at a Dc of 6 A g-1. The FNLDH@FNS//activated carbon (AC) asymmetric SC assembled with FNLDH@FNS (positive electrode) and activated carbon (AC, negative electrode) displays an energy density (Ed) of 36.67 Wh kg-1 and a power density (Pd) of 775.17 W kg-1.

Boosted electrochemical performance of magnetic caterpillar-like Mg0.5Ni0.5Fe2O4 nanospinels as a novel pseudocapacitive electrode material

Ni-incorporated MgFe₂O₄ (Mg_0.5Ni_0.5Fe₂O₄) porous nanofibers were synthesized using the sol-gel electrospinning method. The optical bandgap, magnetic parameters, and electrochemical capacitive behaviors of the prepared sample were compared with pristine electrospun MgFe₂O₄ and NiFe₂O₄ based on structural and morphological properties. XRD analysis affirmed the cubic spinel structure of samples and their crystallite size is evaluated to be less than 25 nm using the Williamson-Hall equation. FESEM images demonstrated interesting nanobelts, nanotubes, and caterpillar-like fibers for electrospun MgFe₂O₄, NiFe₂O₄, and Mg_0.5Ni_0.5Fe₂O₄, respectively. Diffuse reflectance spectroscopy revealed that Mg_0.5Ni_0.5Fe₂O₄ porous nanofibers possess the band gap (1.85 eV) between the calculated value for MgFe₂O₄ nanobelts and NiFe₂O₄ nanotubes due to alloying effects. The VSM analysis revealed that the saturation magnetization and coercivity of MgFe₂O₄ nanobelts were enhanced by Ni²⁺ incorporation. The electrochemical properties of samples coated on nickel foam (NF) were tested by CV, GCD, and EIS analysis in a 3 M KOH electrolyte. The Mg_0.5Ni_0.5Fe₂O₄@Ni electrode disclosed the highest specific capacitance of 647 F g^-1 at 1 A g^-1 owing to the synergistic effects of multiple valence states, exceptional porous morphology, and lowest charge transfer resistance. The Mg_0.5Ni_0.5Fe₂O₄ porous fibers showed superior capacitance retention of 91% after 3000 cycles at 10 A g^-1 and notable Coulombic efficiency of 97%. Moreover, the Mg_0.5Ni_0.5Fe₂O₄//Activated carbon asymmetric supercapacitor divulged a good energy density of 83 W h Kg^-1 at a power density of 700 W Kg^-1.

Embellishing hierarchical 3D core-shell nanosheet arrays of ZnFe2O4@NiMoO4 onto rGO-Ni foam as a binder-free electrode for asymmetric supercapacitors with excellent electrochemical performance

Tailoring hierarchical hybrid core-shell electrodes with impartial microstructural features and excellent electroactive constituents is crucial for the design of high-performance supercapacitors (SCs). Herein, for the first time, we fabricate uniformly aligned porous ZnFe₂O₄ (ZFO) nanosheet arrays onto reduced graphene oxide-garnished conductive Ni foam (rGO-NF) substrates and subsequently embellish the first layer of ZFO nanosheets with morphology-controlled secondary NiMoO₄ nanosheets to achieve a hierarchical 3D core-shell structure of ZnFe₂O₄@NiMoO₄ nanosheet arrays (NSAs) onto rGO-NF for SC applications. Improving the synergistic effect of the core-shell nanoarchitecture with a conductive rGO-NF substrate, the hierarchical 3D ZFO@NMO NSAs tend to have superb electronic conductivity, tailoribility, effective nanoporous channels, and appropriate roadways for rapid ion/electron transfer, which are required for rapid reversible redox reactions, thus reflecting the excellent electrochemical features, including the excellent specific capacitance, good rate performance, and prolonged cyclic performance of the three electrode assemblies for SCs. An asymmetric supercapacitor (ASC) device composed of ZFO@NMO NSAs@rGO-NF as the cathode and MOF-derived hollow porous carbon (MDHPC) as the anode exhibits a high energy density of 58.6 Wh kg^-1 at a power density of 799 W kg^-1 with prolonged cyclic durability (89.6 % after 7000 cycles), thus indicating its potential applicability towards advanced hybrid SCs.